Piano key action testing device



Feb. 23, 1943. HOFMANN PIANO KEY ACTION TESTING DEVICE Filed may a, 1940 3 Sheets-Sheet 1 J. HOFMANN PIANO KEY ACTION TESTING DEVICE Feb. 23, 1943.

Filed May 6, 1940 3 Sheets-Sheet 2 Feb. 23, 1943. HOFMANN- 2,311,752

PIANO KEY ACTION TESTING DEVICE Filed May 6, 1940 s Sheets-Shet 3 Patented F eb. 23, 1943 UNITED STATES PATENT OFFICE PIANO KEY ACTION TESTING DEVICE Josef Hofmann, Newport Beach, Calif. Application May 6, 1940, Serial No. 333,669

7 Claims.

In the playing of a piano, the quality and magnitude of tone is to a considerable extent determined by the action of the piano key. These keys are normally set to operate at a certain amplitude and of course as the piano keys are moved, the resistance to their movement varies as the keys bring the hammers into action.

The purpose of this invention is to graphically determine and show the various degrees of resistance encountered by piano keys on their downward and/or upward movement, and thus establish a line or curve of resistance which will serve as a standard for the best piano touch.

In order to achieve this object, I provide means for applying a predetermined force to actuate a piano key operating through a yieldably disposed element so that variations in resistance to the movement of the piano key under such constant force will be determined and registered either on its downward or its upward movement, or both.

Other objects and advantages of this invention it is believed will be apparent from the hereinafter set forth detailed description of the several modifications thereof illustrated in the accompanying drawings.

In the drawings:

Figure 1 is a side elevation of a piano key action testing device embodying my invention illustrating the same as applied to a piano frame positioned relative to a key thereof.

Figure 2 is an enlarged elevation partially in vertical midsection of the piano key action testing device as illustrated in Figure 1.

Figure 3 s an edge elevation thereof.

Figure 4 is a sectional plan view taken substantially on the line 44 of Figure 2.

Figure 5 is a side elevation mainly in vertical midsection of a further embodiment of my invention.

Figure 6 is a fragmental sectional elevation oi the dash-pot structure embodied in Figure 5.

Figure 7 is a side elevation of a third embodiment of my invention.

Figure 8 is a front elevation of the device as illustrated in Figure '7.

Figure 9 is a sectional view taken substantially on the line 9-9 of Figure 7.

Figure 10 is a detached elevation of the lock lever incorporated in this third embodiment of my invention.

In the modification of my invention as illustrated in Figures 1 to 4, inclusive, the piano testing device of my invention is illustrated as adapted to a piano frame I in position to actuate and test the action of a key 2. key 2 is pivoted at 3 to the frame I.

The piano testing device embodying my invention includes a clamp member 4 by means of which the same may be clamped in position to the frame I. Supported by the clamp 4 is the supporting shaft 5, to the upper end of which there is secured the record holder 6 adapted to removably support a record sheet 1 upon which a curve illustrating the characteristics of the action and movement of a piano key 2 is adapted to be produced through the medium of a marking stylus 8 carried by a lever arm 9.

Means are provided for actuating the lever arm 9 in accordance with the variations in resistance encountered in the movement of the key 2. In this embodiment of my invention the lever 9 carries a key-engaging roller Ill and is pivotally secured at I I to a traveling sleeve I2 mounted upon the supporting shaft 5. A spring I3 is interposed between the lever 9 and the sleeve I2 to maintain a yielding force opposing counterclockwise rotation of the lever 9 around the pivot II. A thumb adjustment screw I4 is provided for determining the initial engaging position of the roller I0 with the surface of the key 2.

Means are provided for moving the sleeve I2 downwardly against the force of the spring to depress the forward end of the key 2 as it is supported upon its pivot 3. In this embodiment of my invention the means provided for moving the sleeve I2 and hence the roller I 0 as it contacts the upper surface of the key 2, includes the reversible electric motor I5 which is secured by suitable securing means IE to the sleeve I2. A shaft I'I rotated by the electric motor I5 carries a worm I8 in position of mesh with the worm pinion or gear I9. Thus movement of the pinion I9 is controlled solely by rotation of the Worm I8 and back-drive is prevented.

The pinion I9 is mounted upon a shaft 20 which is supported in a bearing 2| formed upon the sleeve I2. The shaft 20 at its opposite end carries a ear 22 adapted to mesh With a rack 23 formed on the supporting shaft 5.

A spring 24 provides a resistance to the movement of the sleeve I2 along the supporting shaft 5. A key 25 is provided for holding the shaft 5 from rotation.

The record holder 6 is secured to the reduced section 26 of the shaft 5 through the medium of e. securing thumb-screw 21, the end of which is adapted to project within a recess 28 formed in the reduced section 26 of the shaft 5. Thus by withdrawing the thumb-screw 27 from the recess The piano 28, the record holder may be rotated into a position away from the stylus 8 to permit the insertion or withdrawal of the record cards I.

The electric motor l of the reversing type is connected to any suitable source of electric current through the medium of the current supply cable 29. Interposed within the current supply cable 29 is a rheostat 30 and a reversing switch The rheostat 30 is of any suitable or desirable construction well understood in the art capable of controlling the current supply to the motor 15 to determine its speed of operation.

The reversing switch 3| is provided with the the use of sectional removable weights l5 switch buttons 32 and 33, the actuation of which determines the direction of rotation of the motor l5 and hence the same will drive the pinion i8 in a direction to cause the sleeve l2 to move upwardly or downwardly upon the supporting shaft 5.

The operation of this modification of my invention is: The device is clamped by medium of the clamp 4 to the frame I of the piano in position with reference to the key 2 to be tested. With the device clamped in this position, the thumb-screw I4 is adjusted to position the engaging roller l0 above the upper surface of the key 2 to enable the engaging roller Hi to start its movement before engaging the key. A record card I is positioned in the record holder 6 and the record holder 6 is then rotated to a position where the stylus 3' engages the record card I. The holder 6 is then clamped in this position through the medium of the thumb-screw 21. The rheostat 39 is adjusted to cause the motor shaft 1 to rotate at the desired speed. The down-button 33 is then pressed to complete the electrical circuit to cause the shaft 11 to rotate in a direction to move the sleeve I2 downwardly against the spring 24.

As the sleeve I2 moves downwardly, the roller l0 engaging the key 2 likewise moves downwardly causing the lever 9 to rotate around the pivot H against the pressure of the spring l3.

As long as the resistance to the downward movement imposed by the key 2 remains constant, the lever 9 moves downwardly through a uniform path without rotation around its pivot II. When the resistance to downward movement of the key 2 increases, the roller l0 lags in its movement behind the downward movement of the sleeve 12 by compression of the spring 13 and the lever 9 rotates around the pivot I I The characteristics of the downward movement of the roller H] are thus imposed by the stylus 8 upon the record card I, which record card I produces a graph of the resistance to downward movement of the key 2 and compared with the resistance of the spring [3 as against the distance of travel of the key 2 downwardly. -Any point of sudden increase or change in resistance to the downward travel of the key 2 is thus plotted directly upon the record card 1 forming a permanent record by the characteristic action of the key 2.

It will be obvious from the foregoing that all of the keys 2 of the piano may be correspondingly tested producing the complete record of the piano. If the the action of each key 2 of piano thus tested is one which has been selected because of its satisfactory character of key action, the set of test records I thus made may be preserved and will form a standard for comparison with similar test records produced of other pianos or other keys. Likewise of course thetesting device embodying my inventionmay mounted upon the upper end of the sleeve I2 The resistance to the downward movement of the sleeve 12 in this instance is controlled by the use of a suitable dash-pot 24 The dash- ,pot 2 3 may of course be of any suitable or desirable construction and one particular form is illustrated merely to indicate the complete structure. It includes a piston head 46 carried on the end of the sleeve I2 The supporting shaft 5 is slotted as indicated at M to provide restricted passages for the liquid contained in the cylinder 32 Liquid passing through the passage 4! passes into the chamber 43 formed in the piston and through the ports 44 formed therein. Thus the resistance to flow of the liquid to the opposite sides of the pistons 40 determines the resistance to the downward move ment of the sleeve l2 In order to permit the sleeve l2 to be moved backward to its upper or starting position, means are provided for permitting the liquid to return rapidly to below the piston 40 and this means includes a closure cap 45 for the chamber 53 which is yieldably held in closing position by means of a spring 46 Thus the cap 45 normally closes access to the chamber 43 except when the force is applied to the sleeve I2 to move the same rapidly upward, at which time the cap 45 unseats and permits the rapid return flow of the liquid to below the piston 40. The operation of this embodiment of my invention is substantially the same as that heretofore set forth with the exception that in this case the weights l5 are utilized to simulate the forc ordinarily imparted to the keys 2 by the performer playing the piano.

The embodiment of my invention as illustrated in Figures '7 to 10, inclusive, is similar to that heretofore set forth so that similar parts are indicated with similar numerals with the exponent b added thereto. This embodiment of my invention differs from those heretofore considered in that the force applied to the contacting roller lo is imparted thereto by a spring I5 which is interposed between the control and locking bar50 and the sleeve 2 The lever 9 is-connected to the control and locking bar 50 through the medium of the spring l3. The spring I3 is connected to the end 5t of the bar 50* at one end and to the lever B as indicated at 52* at its opposed end. A dash-pot 24 is carried by the sleeve l2 and is connected at the pivot 53* to the bar 50 In this modification in order to control the movement of the stylus 8 the same is carried upon a stylus arm 59. The stylus arm 54'" is secured upon 'a bushing l55 upon the pin 55 ournaled in the upper end of the lever 9*. Secured to the bushing I55 is a pulley 56 over which there is trained a cable 51 The cable 5'! is also trained over a pulley 53 which isv secured to the pivot II". The lever 9 is journaled on the pivot II The control member 50 15 secured to the, pivot HP. The pivot ll is ro- 2,311,752 tatably mounted on the sleeve 12 The action erence to a piano key, a shaft carried by the supof this device is substantially the same as that heretofore described with the exception that in this case the variation in resistance to the downward travel of the key 2 and the roller Ill is transmitted from the pulley 58 as it fails to rotate with the lever 9 due to an increase in resistance. A stop pin 59* is carried by the lever 9 in position to engage the upper surface of the control member 50 In this modification of my invention, a latch member 60 is pivotally carried by the sleeve I2 in position to engage over the latch end Bl of the control member 50 to maintain the parts in starting position and until the roller lii is contacted upon the upper surface of the key 2 When the parts are thus positioned, the latch member 60 is rotated away from the control member 50* allowing the force to be applied by the spring l5 to depress the roller I ll and hence the key 2'.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details herein set forth, but my invention is of the full scope of the appended claims.

I claim:

1. A piano key action testing device adapted to provide a record of the characteristics of movement of a piano key responsive to pressure, including a record holder, a marking means adapted to produce a mark on a record held by said holder, and means adapted to actuate said marker, said latter means including a key depressing member adapted to contact and move the piano key, and a means adapted to cooperate with the key depressing member to produce a variable movement of said marker responsive to variations in resistance to movement of the piano key over the range of movement of the piano key by said key depressing member.

2. In a piano key action testing device including a supporting means for clamping the testing device in position adjacent a piano key. a piano key contacting member, movable means carried by the support, means for yieldably connecting the contacting member with said movable means, means for moving the movable means downwardly to cause the contacting member to depress the piano key and indicating means carried by the contacting member for indicating variations of travel of the contacting member due to the variations of force required for depressing the piano key.

3. In a piano key action testing device, the combination of a supporting member, means for positioning the supporting member with reference to a piano key, a shaft carried by the sup porting member, a sleeve mounted on the shaft to move longitudinally therealong, a piano key contacting lever adapted to contact a piano key, means for pivotally connecting the lever to said sleeve, means for yieldably resisting pivotal movement of said lever around said pivot, and means for applying a force to move the sleeve downward to move the contacting lever to depress the said piano key.

4. In a piano key action testing device, the combination of a supporting member, means for positioning the supporting member with refporting member, a sleeve mounted on the shaft to move longitudinally therealong, a piano key contacting lever adapted to contact a piano key, means for pivotally connecting the lever to said sleeve, means for yieldably resisting pivotal movement of said lever around said pivot, means for applying a force to move the sleeve downward to move the contacting lever to depress the said piano key, said latter means including an electric motor carried by the sleeve, and gear means connected between the motor shaft and said supporting shaft.

5. In a piano key action testing device, the combination of a supporting member, means for positioning the supporting member with reference to a piano key, a shaft carried by the supporting member, a sleeve mounted on the shaft to move longitudinally therealong, a piano key contacting lever adapted to contact a piano key, means for pivotally connecting the lever to said sleeve, means for yieldably resisting pivotal movement of said lever around said pivot, means for applying a force to move the sleeve downward to move the contacting lever to depress the said piano key, said latter means including a reversible drive electric motor carried by the sleeve, gear means connected between the motor shaft and the supporting shaft, means for controlling the direction of drive of the motor, and means connected in the circuit with the electric motor for controlling its speed of operation.

6. In a piano key action testing device, the combination of a element is carried by the support, means for yieldably connecting the movable element with the key contacting element, means adapted to apply a force to move the movable element to move the key through its normal path of movement, and means operatively associated with the key contacting element for indicating varia tions of downward movement of the key throughout'the said path of movement.

7. In a piano key action testing device, the combination of a supporting member adapted to be positioned adjacent a piano key to be tested, a piano key contacting member, movable means carried by said support and adapted to move the piano key contacting member downwardly to depress a piano key, yieldable means interposed between the movable means and the piano key sistance to movement and over the normal range of movement of the said piano key, and means operably associated with the key contacting member for recording the movement thereof both as to distance and variations in rate of movement caused by varying resistance encountered in the movement of the key.

J OSEF HOFMANN. 

